I would have someone else there when and if you check this and video it with a cell phone for proof.I agree, this does not add up. This is a two minute verification with a creeper. Shift TC to 4 HI, slide under truck, pull linkage off TC and make sure the shift lever is in the 4 HI detent position. If it isn't return to dealer and show them. If it is, it currently isn't the adjustment (but it could have been). If it is adjusted correctly hook up your trailer and video the same conditions it failed on last time. You will either confirm you have a reliable repaired truck, or your third repair for the LL.
This is turning into a way more complicated situation than it has to be. Take the truck, it's still yours. Until the arbitrator says to repurchase or not to repurchase you might as well use it.